P0863 TCM Communication Circuit
OBD-II Trouble Code Technical Description
ASE Certified Technician
TCM Communication Circuit
What does P0863 mean?
This diagnostic trouble code (DTC) is a generic powertrain code and applies to many OBD-II vehicles (1996-newer). That may include but is not limited to vehicles from Dodge, Honda, Volkswagen, Ford, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.
总裁俱乐部appIf your vehicle has stored a code P0863, accompanied by a malfunction indicator lamp (MIL), it means that the powertrain control module (PCM) has detected an abnormal electrical condition in the transmission control module (TCM) communication circuit.
While some transmission control modules (for OBD-II equipped vehicles) are integrated into the PCM, most are stand-alone components. TCM related codes may also be stored as P-codes, B-codes, or even U-codes, depending on vehicle make and model. If a P0863 code is stored, there is a good chance that there are other PCM and/or TCM codes stored as well. Antilock braking system (ABS) codes may be stored, too.
Electronic transmission control systems in OBD-II equipped vehicles are controlled using a network of computers (called control modules). This involves constant communication between the various control modules via the controller area network (CAN).
The PCM utilizes input signals from multiple engine and transmission sensors to calculate automatic transmission shift strategy. A high-pressure pump (inside the transmission) forces fluid through the valve body and into the sprag assembly; in addition to lubricating and cooling the transmission. The high-pressure fluid allows the clutches to separate from the sprag momentarily so that the gear ratio may be changed smoothly. One or more electronic pressure control (EPC) solenoids help to regulate fluid pressure.
Electronic pressure (EP) sensors provide the PCM with pertinent data regarding fluid pressure at various points in the transmission.
总裁俱乐部appElectronic shift solenoids are used to interrupt the flow of high-pressure fluid so that the transmission shifts gears when commanded. The PCM uses voltage input signals from the transmission input speed sensor and transmission output speed sensor to determine if the transmission is shifting efficiently.
As with many other automatic transmission malfunctions, a transmission control system code may be caused by either an electrical or mechanical failure. If the PCM detects a malfunction which demands MIL illumination, a code P0863 will be stored and a MIL may be illuminated.
An example of a typical TCM transmission control module
What is the severity of this DTC?
If this code is stored, you may have noticed that your transmission shifts much more harshly than normal. If your vehicle has exhibited a code P0863 , it should be diagnosed as soon as possible.
What are some of the symptoms of the code?
总裁俱乐部appSymptoms of a P0863 trouble code may include:
- Erratic transmission shift patterns
- Failure of the transmission to shift
- Diminished fuel efficiency
- Transmission slippage
- Delayed transmission engagement
- Other transmission related codes
- ABS disabled
What are some of the common causes of the code?
总裁俱乐部appCauses for this code may include:
- Transmission sensor failure
- Vehicle speed sensor failure
- Open or shorted circuits in the CAN harness
- Mechanical transmission failure
- Defective TCM, PCM, or programming error
What are some P0863 troubleshooting steps?
总裁俱乐部appYou will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of reliable vehicle information in order to accurately diagnose a code P0863. An oscilloscope can also prove very helpful in diagnosing various sensor outputs.
You may save yourself time by searching for technical service bulletins (TSB) that replicate the code stored, vehicle (year, make, model, and engine), and symptoms exhibited. This information may be found in your vehicle information source. If you find the right TSB, it could yield a speedy solution to your diagnosis.
After you connect the scanner to the vehicle diagnostic port and retrieve all stored codes and pertinent freeze frame data, write the information down (in case the code proves to be an intermittent one). After that, clear the codes and test drive the vehicle until one of two things happens; the code is restored or the PCM enters readiness mode.
The code may be more difficult to diagnose if the PCM enters readiness mode at this point, because the code is intermittent. The condition which caused the P0863 to be stored may need to worsen before an accurate diagnosis can be made. If the code is restored, continue with the diagnosis.
You may obtain connector face views, connector pinout charts, component locator charts, wiring diagrams, and diagnostic flow charts (pertaining to the code and vehicle in question) using your source of vehicle information.
Perform a visual inspection of related wiring and connectors. Repair or replace wiring that has been cut, burned, or damaged.
Use the DVOM to test voltage and ground circuits at the TCM and/or PCM. If no voltage is detected, check system fuses. Replace blown or otherwise defective fuses as required and retest.
If voltage and ground are detected at the TCM, test the corresponding circuit at the PCM connector. If no voltage is detected there, suspect an open circuit between the component in question and the PCM. If voltage is discovered there, suspect a defective TCM. PCM, or a programming error.
- Most communication error codes can be attributed to a programming issue
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